Thanks to Facebook's strategy to collaborate with the likes of RIM (BlackBerry), Palm, and Microsoft to create its mobile applications, the software isn't identical on any two operating systems. What does carry over are Facebook's core features--the news feed, status, and photo updates, notifications, and friend requests. Also your personal wall, info, and photos, your friends list, and so on.
It's noteworthy that the phone's form factor may affect how you navigate. On a tall, thin phone, flipping the screen horizontally will show the full width of the app, but not the depth. The vertical view condenses the navigation icons up top but truncates the secondary navigation bar just below, so you'll need to scroll to the right to see the photo tab, for instance.
Beyond the basics, Microsoft and Facebook have implemented some unique and useful functionality tailored to this platform. You're able to upload photos and videos to Facebook's news feed, either from your media library, or by spanning or recording them in real-time. There's also an icon of a phone on the navigation bar that displays the names and numbers of buddies who have populated their profiles with their digits. With this list, you can call, text, or send a message to their Facebook in-box. While the app could use some visual polish and is missing the ability to update your profile picture from the phone, Microsoft has risen to the occasion with the substance of this app, and the effort shows.